1. Field of the Invention
This invention relates to improvements in apparatus for carrying out the stereoscopic observation of a sample surface, and more particularly to apparatus capable of tridimensionally measuring the distance between two arbitrary points on the sample surface. More specifically, this invention relates to apparatuses, for example, a scanning electron microscope (SEM), X-ray micro analyzer (XMA), ion micro analyzer (IMA), ultrasonic microscope etc., wherein a sample surface is irradiated by an energized beam such as electron beam, ion beam, light beam, X-ray beam and ultrasonic beam while being scanned, wherein a secondary radiation thus obtained, such as secondary electrons, transmitted electrons, secondary ions and X-rays, is detected and wherein the scanning image of the sample surface is displayed by making the detected signal a video signal, characterized in that marks for indicating positions are superposed and displayed at two arbitrary points on the displayed image and that the microscopic and tridimensional distance between the two points given by the marks is measured and displayed.
2. Description of the Prior Art
In measuring a minute distance on a sample surface with a scanning electron microscope (SEM) or the like, it has heretofore been common practice to superpose and display a measurement scale on a sample image expandedly displayed. With such method, a satisfactory measurement precision is not attained on account of the distortion of the displayed image, the error of the magnification, etc. Moreover, since the size of the measurement scale changes in dependence on the magnification, there is the inconvenience that the size of the measurement scale need be recalculated each time the magnification changes.
There has hitherto been known apparatus wherein the magnified image of a sample surface by an optical microscope is photographed by a TV camera and displayed on a Braun tube, two parallel straight lines are superposed and displayed on the image, and the distance between the two straight lines is digitally indicated. Even with this apparatus, the tridimensional distance between two arbitrary points on the sample surface cannot be measured in real time.
Further, there has been proposed a stereo scanning electron microscope (stereo SEM) which enables the stereoscopic observation of a sample surface by changing the irradiation angle of a primary electron beam on a sample (refer to U.S. Pat. No. 3,585,382). Even in this apparatus, it is not conducted to automatically measure the tridimensional distance between two arbitrary points on the sample surface in real time.